OPEN ACCESS International Journal of Aquatic Science ISSN: 2008-8019 Vol. 5, No. 2, 145-153, 2014

Parasites of wild glass and cultured elvers of the giant mottled (Anguilla marmorata Quoy and Gaimard, 1824) in Vietnam

Dung The Vo*, Cong Van Chu, Dung Thi Vo, Glenn Allan Bristow

Research Institute for Aquaculture No.3; 33 Dang tat, Nha Trang, Vietnam

Received: 26 September 2013 Accepted: 27 November 2013 Published: 30 June 2014

Abstract: This article reports a survey of parasites in wild glass eels following them through culture to elvers in over-flow and re-circulating water systems in Vietnam. The results show that wild glass eels are infected with three parasitic species (Trichodina sp., Ichthyophthirius multifilis and Pseudodactylogyrus anguillae). Eels in re-circulating systems are infected with three parasites (Trichodina acuta, Trichodina sp., and Pseudodactylogyrus anguillae). Seven parasitic species were found on/in eels in the over-flow system (T. acuta, Trichodina sp., I.multifilis, P. anguillae, Pseudodactylogyrus bini, Centrocestus formosanus (metacercaria), and, Haplorchis taichui (metacercaria). Two parasites, Trichodina sp., and P. anguillae, were found on wild glass eels and elvers in both rearing systems. T. acuta had the highest prevalence (57.3%) in the recirculating system. P. bini had the highest prevalence (56.1%) in the over-flow system. The prevalence of Trichodina sp. infected fish in the recirculating system was 39.6%. That of C. formosanus (metacercaria) was 10.6% in the over-flow system. The prevalence of other parasites in all habitats was less than 10.0%. Two out of 3 parasites found in the re-circulating system had higher prevalence than those in the over-flow system. Results show that elvers reared in over-flow water systems had more parasites than wild glass eels or those reared in recirculating water system. Key words: eel culture, Anguilla marmorata, parasites, Vietnam

Introduction The glass eel is an early developmental are nocturnal, and feed on a wide range of prey, stage in the eels. The giant mottled eel, Anguilla especially , fish and (Skelton, 1993). marmorata Quoy & Gaimard, 1824, has the Adult giant mottled eels offshore and widest distribution among anguillid eels, when the eggs hatch a larva called a occurring throughout almost the entire Indo- emerges. The leptocephali spend Pacific area (Tesch, 2003). Like other anguillids, approximately 114-132 days drifting in the adults live in freshwater or estuarine habitats, plankton before migrating to river mouths as

() [email protected] The Vo et al. (2014) Parasites of wild glass eels and cultured elvers of the giant mottled …

glass eels (Arai et al., 2002), where they Dong Province, the rearing systems use fiber undergo metamorphosis into elvers in the glass tanks with re-circulated water. Original freshwater. water is filtered through sand, then through a The giant mottled eel has been widely bio-filter before re-use. The system can replace cultured (‘grown-out’) in Vietnam for many 100% water in rearing tanks within 2 hours. years. However, there is no artificial breeding Temperature in the water varies between 13– technology available at present for the 18°C. production of glass eels. Therefore, Vietnamese Recently, eel production has declined for eel culture has to rely on wild-caught glass eels unknown reasons. In an attempt to determine if from the Ba River in Phu Yen Province in the parasites could be a contributing factor, this South Centre of Vietnam (Cong et al., 2012). In study was designed to compare parasite the Ba River, glass-eels swim upstream during prevalence in glass eels collected from the wild the night towards a dam as part of their in Phu Yen Province and elvers from the over- migration, the water temperature in the river flow and re-circulating systems in Khanh Hoa varies from 18-24°C. Close to the dam, local and Lam Dong Provinces, respectively. people use scoop nets made of mosquito netting to catch wild glass eels and keep them Materials and Methods in clean, fresh water at a temperature of 18– Sources of glass eels and elvers 20°C before selling them to fish farmers (Cong Wild glass eels were caught in the mouth of et al., 2012). Ba River in Phu Yen Province. Then move to At the farms, the glass eels are grown in Khanh Hoa and Lam Dong Provinces for rearing. either cement or composite tanks for about 3–6 The majority of the glass eels were bathed with months before being sold for grow-out as formalin (30 ppm) to treat for ectoparasites elvers. In Khanh Hoa Province, the rearing before being introduced into the rearing systems consist of an over-flow system using systems. They were in rearing systems for water from a reservoir. The water is filtered about 1 to 2 months before sampling for through sand and flows into a cement tank parasite examination. Subsamples of the glass system, where the eels are reared. Each tank eels packed in nylon bags inflated with oxygen has a volume of 2 m3. Water continuously and filled with clean freshwater and transported passes through the rearing systems with a to the Research Institute for Aquaculture No.3 constant flow rate which is sufficient to change for parasite examination. The water occupied 100% of the water within 4 hours. The 1/3 of the bag volume and temperature in the temperature varies between 19–27°C. In Lam bags varied between 18–22°C.

Int. J. Aqu. Sci; 5(2): 145-153, 2014 146 The Vo et al. (2014) Parasites of wild glass eels and cultured elvers of the giant mottled …

Elvers were collected from the respective kept in 3 m3 cement tanks before being rearing systems in Khanh Hoa and Lam Dong examined for parasites within 24 hours of Provinces. They were transported from the arrival. The tanks were constantly supplied with collection sites to the Research Institute for clean, fresh water and 15–20 fish collected at a Aquaculture No. 3 (RIA3) in Nha Trang City, time to avoid crowding in the tanks. Table 1 Khanh Hoa Province, in the same manner as the shows the number, length, and weight of wild glass eels above. glass eels and reared elvers collected from At RIA3, both glass eels and elvers were different sites.

Tab. 1: Number, length and weight of wild glass eels and elvers collected from different sites.

Fish number Mean length ± SD Mean weight ± SD Sampling sites (specimens) (Range) (Range)

Phu Yen 48.4 ± 3.5 0.13 ± 0.05 57 (Wild glass eel) (44.0-58.0) (0.10-0.20) Khanh Hoa 57.4 ± 4.9 0.25 ± 0.07 66 (Elvers) (45.0-65.0) (0.10-0.32) Lam Dong 55.2 ± 6.3 0.24 ± 0.08 96 (Elvers) (45.0-63.0) (0.10-0.30)

Parasite examination and identification ed the recommendations in Bush et al. (1997). Each eel was scraped to collect external The prevalence of each parasitic species in each mucus. In addition, they were dissected, the host group was compared between different gills, liver, gall bladder and viscera and sites using a Chi-square test with Yates examined for the presence of parasites. All correction being employed if 5 or more fish parasites found were fixed following the were infected. When less than 5 fish were methodologies of Lom and Dykova (1991) and infected, the Fisher-exact test (two tails) was Berland (2005). They were then photographed, used, significance level of α = 0.05. drawn and measured for aid in identification. Results Data analysis Prevalence of parasites from wild glass eels, Standard parasitological parameters follow- and elvers from over-flow and re-circulating

Int. J. Aqu. Sci; 5(2): 145-153, 2014 147 The Vo et al. (2014) Parasites of wild glass eels and cultured elvers of the giant mottled …

systems is presented in Table 2. Three parasitic over-flow systems, while this parasite was not species infected wild glass eels, 7 parasitic found in either elvers from re-circulating species were found from elvers in over-flow systems or wild glass eels. P. angu1illae was systems (Khanh Hoa Province) and 3 parasitic found in both over-flow and re-circulating species found from elvers in re-circulating systems, with a prevalence of 7.6% and 6.3 %, systems (Lam Dong Province). The prevalence respectively. Ichthyophthirius multifilis and of T. acuta was 57.3% in re-circulating metacercaria of C. formosanus were found only systems, and 33.3% in over-flow systems. The in over-flow systems, at prevalence of 3.0% prevalence of Trichodina sp. was 39.6% of and 10.6%, respectively. Metacercaria of H. elvers in re-circulating systems, 1.5% of elvers taichui were found in elvers from over-flow in over-flow systems and 1.7% in wild glass systems with a prevalence of 9.0%. eels. The prevalence of P. bini was 56.1% in

Tab. 2: Prevalence of parasites from wild glass eels, and elvers from over-flow and re-circulating systems.

Number fish infected/number fish examined (%)

Parasites Over-flow Re-circulating Wild system system

Trichodina acuta 0/57 (0.0) 22/66 (33.3) 55/96 (57.3) Trichodina sp. 1/57 (1.7) 1/66 (1.5) 38/96 (39.6) Ichthyophthirius multifilis 2/57 (3.4) 2/66 (3.0) 0/96 (0.0) Pseudodactylogyrus anguillae 1/57 (1.7) 5/66 (7.6) 6/96 (6.3) Pseudodactylogyrus bini 0/57 (0.0) 37/66 (56.1) 0/96 (0.0) Centrocestus formosanus (Metacercariae) 0/57 (0.0) 7/66 (10.6) 0/96 (0.0)

Haplorchis taichui (Metacercariae) 0/57 (0.0) 6/66 (9.0) 0/96 (0.0)

Table 3 shows statistical comparison of the bini, C. formosanus, and metacercariae of H. prevalence of the parasites found among glass taichui were statistically significantly higher on eels and elvers. Results of comparison between elvers (P<0.05), while the prevalence of wild glass eels (Phu Yen Province) and elvers Trichodina sp., I. multifilis and P. anguillae were from over-flow systems (Khanh Hoa Province) not statistically significantly different between showed that the prevalences of T. acuta, P. eels from the two sites.

Int. J. Aqu. Sci; 5(2): 145-153, 2014 148 The Vo et al. (2014) Parasites of wild glass eels and cultured elvers of the giant mottled …

Tab. 3: Statistical comparison of the prevalence of the parasites found among glass eels and elvers.

Wild (Phu Yen) vs. Wild (Phu Yen) vs. Over-flow (Khanh Hoa) vs.

Parasites over-flow re-circulating re-circulating (Khanh Hoa) (Lam Dong) (Lam Dong)

P value P value P value

Trichodina acuta <0.01 <0.01 0.09 Trichodina sp. 1.00 <0.01 <0.01 Ichthyophthirius multifilis 1.00 <0.01 0.17 Pseudodactylogyrus anguillae 0.21 0.25 0.76 Pseudodactylogyrus bini <0.01 <0.01 Centrocestus formosanus (Metacercariae) 0.01 <0.01 Haplorchis taichui (Metacercariae) 0.03 <0.01

Results of comparison between wild glass The parasite composition eels (Phu Yen Province) and elvers from re- The parasites of eels have been studied circulating systems (Lam Dong Province) comprehensively in Europe, while in Vietnam, showed that the prevalence of three parasitise only two references mention parasites of eels (T. acuta, Trichodina sp., and Ichthyophthirius (Arthur and Bui, 2006; Ha and Bui, 2007). multifilis) were statistically significantly higher in These documents report 4 parasitic species: 1 elvers. The prevalence of P. anguillae was not nematode, 1 monogenean, and 2 protozoa. This statistically different between wild glass eels paper finds three parasites on wild glass eels, and elvers from re-circulating systems. and, 7 and 3 parasitise from elvers in over-flow The results show that there are statistically systems and re-circulating systems, significant differences between prevalence of 4 respectively. Sasal et al. (2008) reported 8 taxa parasitise from over-flow systems and re- of parasites found from giant mottled eel on the circulating systems.The prevalence of Island of Reunion, including Pseudodactylogyrus Trichodina sp. was higher in elvers from re- anguillae, P. bini, Anguillicoloides crassus, circulating systems, while that of C. Paraquimperia africana, Acanthocephalus formosanus, P. bini and H. taichui were higher reunionensis, Bothriocephalus claviceps, and, in elvers from over-flow systems. Prevalences cestode and nematode larvae. Only two of of other parasites were not statistically these parasites (P. anguillae and P. bini) were significantly different. found in this study. Trichodina acuta is a non-host specific ciliate Discussion found worldwide on various fish species such as

Int. J. Aqu. Sci; 5(2): 145-153, 2014 149 The Vo et al. (2014) Parasites of wild glass eels and cultured elvers of the giant mottled …

Cyprinus capio, Carassius auratus, Pseudodactylogyrus bini. This species was later Oncorhynchus mykiss, Salmo trutta, Phoxinus found from different eels in various areas, phoxinus (Gaze and Wootten, 1998); Anguilla Hayward et al. (2001) reported it from the anguilla (Imai et al., 1991). In Vietnam, this American eel Anguilla rostrata in North America. species has been reported from Pangasius Ogawa and Egusa (1976) reported it from the micronemus, P. hypophthalmus, Cirrhina European eel A. anguillae. This is the first mrigala, Labeo rohita, Cyprinus capio, record of this species in Viet Nam, and the first Orechromis niloticus niloticus, record on A. marmorata. Ctenopharyngodon idellus (Arthur and Bui, Centrocestus formosanus is a zoonotic 2006; Ha and Bui, 2007), this is the first record parasite found in many freshwater fish species on A. marmorata. world-wide. In Vietnam, metacercaria of this Ichthyophthirius multifilis is a common species are found in Cyprinus carpio, Clarias diseased causing ciliate of many freshwater fish fuscus, C. macrocephalus, C. batrachus, species of various areas in the world (Lom and Hypophthalmichthis harmandii, Barbodes Dyková, 1992). Ha and Bui (2007) reported it gonionotus, Monopterus albus, Labeo rohita, from A. marmorata in Vietnam. Cirrhinus migrala, Catla catla, Osphronemus Pseudodactylogyrus anguillae was originally gorami, Oreochromis niloticus, described from the Anguillae Ctenopharhyngodon idellus, Colossoma japonica as Dactylogyrus bini Kikuchi (1929), macropomum (Ha and Bui, 2007); in after several systematic changes, it finally Aristichthys nobilis, Cyprinus carpio, became Pseudodactylogyrus anguillae. Today, Ctenopharhyngodon idellus, Cirrhinus migrala, this monogenea is reported from various Labeo rohita, Hypophthalmichthis molitrix, species of eel. Marcogliese and Cone (1993) Oreochromis niloticus (Chi et al., 2008); and, in reported it from the American eel Anguilla Pangasiannodon hypophthalmus, Anabass rostrata. Sasal et al. (2008) reported it from testudineus, Ctenopharhyngodon idellus, Anguilla mossambica and A. marmorata from Cyprinus carpio (Thien et al., 2007). This is the Reunion Island. Ha and Bui (2007) reported it first record from A. marmorata. from Oxyeleotris marmoratus, Anguilla japonica Haplorchis taichui is a zoonotic trematode. It and A. marmorata in Viet Nam. has been intensively studied in many countries. Pseudodactylogyrus bini was originally Its metacercariae have been confirmed to have described from the Japanese eel Anguillae a wide range of fish hosts and wide japonica as Dactylogyrus bini Kikuchi (1929), geographical distribution, and have been Gusev (1965) re-decribed it as reported in different fish species in Vietnam. Ha

Int. J. Aqu. Sci; 5(2): 145-153, 2014 150 The Vo et al. (2014) Parasites of wild glass eels and cultured elvers of the giant mottled …

and Bui (2007) reported them from Silver carp 0.05) between parasite prevalence from eels of (Hypophthalmichthys harmandi), Grass carp 3 different systems and 7 cases with no (Ctenopharryngodon idellus), Common carp significant difference found. (Ciprinus carpio), Climbing perch (Anabas The fish in this study collected from different testudineus). Thien et al. (2009) found them in systems, which could have had different organic Giant gourami (Osphronemus gourami), Kissing and inorganic contents, for ex. some organic gourami (Helostoma temmincki). Adults have contents could be higher in over-flow systems been found in dog, cat and humans in Vietnam, than those in re-circulating systems. This might Taiwan, The Philippines, Bangladesh, Palestine, be one of the reasons for the differences of China, Thailand (Chai et al., 2005). Dung et al. prevalences. The results show that wild glass (2007) confirmed its presence in human in eels were infected with 3 species at low Vietnam. This is the first record from A. prevalence (1.7 – 3.4 %), while elvers in re- marmorata. circulating systems were also infected with 3 species, but at much higher prevalence (6.3 – The prevalence of parasites of eels from 57.3 %). Elvers in overflow systems were different sites infected with 7 species and prevalence varied Several studies have reported different between 1.5 and 56.1 %. The wild glass eels infection of fish with Trichodina spp. due to had recently entered the river mouth, where different habitat conditions. Madsen et al. they encountered a sudden reduction in salinity; (2000) showed that eels reared in water that this probably reduced any ectoparasites that had high contents of organic parameters, low they brought from the sea. They had not been concentration of nitrate and high pH suffered long enough in the brackish/fresh water to be more problems with Trichodina jadranica than infected with other parasites. Both factors may eels in water that had low contents of organic help explain why the wild glass eels were parameters, high concentration of nitrate and infected with only 3 species at low prevalence. low pH. Ogut and Palm (2005) showed that the There were no statistically significant prevalence of Trichodina spp. on the gills of differences (P>0.05) between the prevalence of Whiting (Merlangius merlangus) varied wild glass eels and elvers from over-flow seasonally; and, that its variation correlated systems infected with the same parasitic with the concentration of nitrite, nitrate, species (Trichodina sp., I. multifilis, and P. phosphate, oxygen, and, water temperature. anguillae). The over-flow systems use a Results of this study show that in 11 out of reservoir water source run through a sand filter, 18 cases there are significant differences (P < thus many environmental parameters might be

Int. J. Aqu. Sci; 5(2): 145-153, 2014 151 The Vo et al. (2014) Parasites of wild glass eels and cultured elvers of the giant mottled …

similar to those in the habitat where the wild systems. glass eels had been collected. References There was no statistically significant  Arthur J.R. and Bui T.Q. (2006) Checklist of the parasites difference in prevalence of P. anguillae of wild of fishes of Viet Nam. FAO Fisheries Technical Paper glass eels and elvers from re-circulating 369/2. FAO, Rome. systems. This parasite is not commonly found in  Berland B. (2005) Whole mounts, Occational peblication Vietnam, and its prevalence was very low on No. 1 Institute of Oceanography, Kolej Univesity Sains dan Teknologi Malaysia (Kustem). the fish collected from the two systems, this  Bush A.O., Lafferty K.D., Lotz J.M. and Shostak A.W. could make statistical detection differences (1997) Parasitology meets ecology on its own terms: difficult, or, there may truly be no statistically Margolis et al. revisited. J. Parasitol., 83: 575-583.  significant differences in this case. Chai J.-Y., Murrell K.D. and Lymbery A.J. (2005) Fishborne parasitic zoonoses: status and issues. Int. J. Results also show that Trichodina sp. Parasitol., 35: 1233-1254. prevalence was not statistically significant  Chi T.T.K., Dalsgaard A., Turnbull J.F., Tuan P.A. and different between wild glass eels in Phu Yen and Murrell K.D. (2008) Prevalence of Zoonotic Trematodes elvers from Khanh Hoa Province; in these two in Fish from a Vietnamese Fish-Farming Community. J. Parasitol., 94: 423-428. provinces, water temperatures are almost  Cong C.V., Hoan N.T, Khuong B.X., (2012) Final report identical. Comparison between elvers from Lam of the research project “Establishing industrial scale Dong and Khanh Hoa, as well as between elvers nursing proceeder of eels A. marmorrata”. Libarary of from Lam Dong and wild glass eels from Phu Research Institute for Aquaculture No.3, 80 pp.  Dung D.T., De N.V., Waikagu J., Dalsgaard A., Chai J.-Y., Yen, demonstrated statistically significant Sohn W.-M. and Murrell K.D. (2007) Fishborne zoonotic differences in both cases. Lam Dong has lower intestinal trematodes, Vietnam. Emerg. Inf. Dis., 13: water temperatures than the other two 1828-1833.  provinces. Thus temperature might have Gaze W.H. and Wootten R. (1998) Ectoparasitic species of the genus Trichodina (Ciliophora: Peritrichida) important effect on the prevalence of parasites parasitising British freshwater fish. Fol. Parasitol., 45(3): in eels in this case. 177-190. -Both wild glass eels and elvers were infected  Ha K. and Bui T.Q. (2007) The Parasites of freshwater with parasites. Elvers reared in over-flow fish in Vietnam. Publishing house of Science and Techniques. Hanoi. (In Vietnamese). systems were infected with significantly more  Hayward C.J., Iwashita M., Ogawa K. and Ernst I. (2001) parasitic species than wild glass eels or elvers Global spread of the eel parasite Gyrodactylus anguillae reared from re-circulating systems. (Monogenea). Bio. Inv., 3(4): 417-424.  -Elvers reared in over-flow water systems had Imai S., Miyazaki H. and Nomura K. (1991) Trichodinid species from the gill of cultured Japanese eel, Anguilla higher prevalences of parasites than wild glass japonica, with the description of a new species based on eels or elvers reared in re-circulating water light and scanning electron microscopy. Eur. J. Pro.,

Int. J. Aqu. Sci; 5(2): 145-153, 2014 152 The Vo et al. (2014) Parasites of wild glass eels and cultured elvers of the giant mottled …

27(1): 79-84. 42: 395-404.  Kikuchi H. (1929) Two new species of Japanese  Ogut H. and Palm H.W. (2005) Seasonal dynamics of trematodes belonging to Gyrodactylidae. Ann. Zoo. Jap., Trichodina spp. on whiting (Merlangius merlangus) in 12: 175-186. relation to organic pollution on the eastern Black Sea  Lom J. and Dyková I. (1992) Protozoan Parasites of coast of Turkey. Parasitol. Res., 96: 149-153. Fishes. Developments in Aquaculture and Fisheries  Sasal P., Taraschewski H., Valade P., Grondin H., science, Volume 26. Elsevier Science Publishers B.V. Wielgoss S. and Moravec F. (2008) Parasite communities  Madsen H.C.K., Buchmann K. and Mellergaard S. (2000) in eels of the Island of Reunion (Indian Ocean): a lesson Association between trichodiniasis in eel (Anguilla in parasite introduction. Parasitol. Res., 102: 1343-1350. anguilla) and water quality in recirculation systems.  Thien P.C., Dalsgaard A., Nhan N.T., Olsen A. and Aquaculture, 187: 275-281. Murrell K.D. (2009) Prevalence of zoonotic trematode  Marcogliese D.J. and Cone D.K. (1993) What metazoan parasites in fish fry and juveniles in fish farms of the parasites tell us about the evolution of American and Mekong delta, Vietnam. Aquaculture, 295: 1-5. European eels. Evolution, 47: 1632-1635.  Thien P.C., Dalsgaard A., Bui N.T., Olsen A. and Murrell  Ogawa K. and Egusa S. (1976) Studies on eel K.D. (2007) Prevalence of fishborne zoonotic parasites in pseudodactylogyrosis-I. Morphology and classification of important cultured fish species in the Mekong Delta, three eel dactylogyrids with a proposal of a new species, Vietnam. Parasitol. Res., 101: 1277-1284. Pseudodactylogyrus microrchis. Bull. Jpn. Soc. Sci. Fish.,

Int. J. Aqu. Sci; 5(2): 145-153, 2014 153